A tine portion for an implantable medical device includes a hook segment and a distal segment terminated by a tissue-piercing tip, wherein the distal segment extends from the hook segment to the tip. The hook segment, which is elastically deformable from a pre-set curvature, has one of: a round cross-section and an elliptical cross-section, while the distal segment has a flattened, or approximately rectangular cross-section. One or a pair of the tine portions may be integrally formed, with a base portion, from a superelastic wire, wherein the base portion is configured to fixedly attach to the device, for example, being captured between insulative members of a fixation subassembly.